[3] It is one of the few facilities in the San Diego water supply system that relies entirely on local runoff.

Morena Dam is located in the Cleveland National Forest at the headwaters of Cottonwood Creek, about 40 miles (64 km) east of downtown San Diego.

Water released from Morena Dam travels several miles down Cottonwood Creek to Barrett Lake, where it is diverted to Lower Otay via the 14-mile (23 km) long Dulzura Conduit.

[9] A bond issue was approved in 1896 for construction of Morena Dam, which would form the highest and most remote of the reservoirs.

The initial construction was fraught with problems caused by leakage and poor engineering, and work stopped in April 1898.

[3] Because the dam was built in a high mountain area with some of the highest annual rainfall in San Diego County, it was anticipated that its reservoir would fill every year.

However, the early 1900s saw continuous drought conditions in Southern California, and the reservoir did not fill to more than a third of its capacity in the first few years of operations.

[4] In 1916, the city of San Diego hired Charles Hatfield, a man known as the "Rainmaker", who had offered to fill Morena Reservoir at a cost of $10,000.

Rising at a peak rate of two feet (0.6 m) per hour, Morena Reservoir filled and spilled on January 26, a mere 5 inches (13 cm) from the top of the dam.